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I am trying to design my first wireless digital communication system. I am going to use non-coherent procedure for detection.

Say I am sending a particular bit $$T_b=5secs$$

Now at transmitting side I start the bit time from some particular (may be arbitrary) reference time. But at the receiving side from when to start measuring this particular bit. As my system is non-coherent, I have no clue when to start the bit measuring process. The book does not say much on that.

Any clue would be greatly appreciated.

niki_t1
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  • Hint: if you write complete comprehensible sentences and include a concrete question in your posting you may get an useful answer. – Curd Feb 10 '17 at 09:06
  • I think you need to read more of the book, before you try to ask a question. The question is non-coherent, I have no clue where to start the answering process. – Neil_UK Feb 10 '17 at 09:20
  • Detection and framing (synchronisation) are pretty much orthogonal concepts, maybe the book covers synchronisation in another chapter. –  Feb 10 '17 at 11:51
  • @user3001408 you may want to change your profile name – Voltage Spike Feb 10 '17 at 17:49

1 Answers1

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Assuming you have a modulator, a usable wireless channel, a receiver and a demodulator, an example of a simple communication synchronization technique is to use what is known as a preamble. The preamble is sent prior to sending real data (pay load). In between preamble and payload is a header. So, you transmit: -

  • Preamble (a series of bytes that are recognizable from payload data or the header)
  • A header - marks the end of the preamble and tells the receiver that the preamble has finished and that the next byte is data. It may also tell the receiver how many bytes are contained in the pay-load.
  • Data (might be fixed length or variable length)
  • Checksum - this allows the receiver to compare (or measure) that what was transmitted is the same as what was received.

Because the preamble is "special" it can be recognized from pay-load data and hence, when the receiver sees it, the sync process begins. Because the preamble is a repeated "special" bit pattern, it doesn't matter if the receiver misses the first one or two repeated patterns.

If the receiver doesn't see preamble then it waits until it does. This means that real pay-load data can be missed but that is the price you have to pay for usable and reliable data communications. Here's an example using FM modulation: -

enter image description here

See also this EE page for a slightly more comprehensive answer.

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